1. Field of the Invention
The present invention relates to a cleaning device for electrophotographic apparatus, an electrophotographic apparatus, a cleaning method for cleaning a light receiving member of the, electrophotographic apparatus, and an electrophotographic process having the cleaning method and, more particularly, to a cleaning device for implementation of scrape-cleaning using a cleaning blade, an electrophotographic apparatus therewith, a cleaning method for cleaning a light receiving member of the electrophotographic apparatus, and an electrophotographic process having the cleaning method.
2. Related Background Art
Materials for the light receiving member used as an electrophotographic, light receiving member include a variety of materials suggested heretofore, for example, such as inorganic materials including selenium, cadmium sulfide, zinc oxide, amorphous silicon (hereinafter referred to as a-Si), and so on, or organic materials. Among these materials, non-monocrystalline deposited films containing the silicon matrix, typified by a-Si, for example amorphous deposited films of a-Si containing hydrogen and/or halogen (for example, fluorine, chlorine, or the like) for compensating dangling bonds were suggested as high-performance, highly durable, and nonpolluting light receiving members, some of which are in practical use. For example, U.S. Pat. No. 4,265,991 discloses the technology of the electrophotographic, light receiving member whose photoconductive layer is formed mainly of a-Si. Further, for example, Japanese Patent Application Laid-Open No. 60-12554 discloses a surface layer containing carbon and halogen atoms on a surface of the photoconductive layer made of amorphous silicon containing silicon atoms.
As methods for forming the silicon-based non-monocrystalline deposited films, there are many known methods, including sputtering methods, methods of decomposing a source gas by heat (thermal CVD), methods of decomposing the source gas by light (photo CVD), methods of decomposing the source gas by a plasma (plasma CVD), and so on. Among them, the plasma CVD methods, which are methods for decomposing the source gas by glow discharge or the like generated by direct current or high-frequency wave (RF or VHF) or microwave to deposit a deposited film on a desired substrate of glass, quartz, heat-resistant synthetic resin film, stainless steel, aluminum, or the like, are in a very advanced stage of practical application at present, not only to the methods for forming the amorphous deposited films for electrophotography etc., but also to methods for forming deposited films for the other uses, and a variety of devices therefor also have been suggested heretofore.
Further, as to the application to the light receiving members for electrophotography, there are strong desires for improvement in the quality of film and in the processing performance in recent years and various ideas and means have been studied.
Particularly, a plasma process using high-frequency power has various advantages of high stability of discharge, applicability to formation of insulating materials such as oxide films, nitride films, and the like, and so on, and thus is used because of the advantages.
With the light receiving members, there are recent demands for improvement in electrophotographic characteristics ready for high-speed operation and for the image quality of higher definition. Under such circumstances, in addition to the improvement in the characteristics of the light receiving members, the grain sizes of developers are being decreased to smaller sizes and commonly used developers have a weight average diameter by a coulter counter or the like in the range of 5 to 8 .mu.m.
There are also various types of developers, depending upon uses, and more models have been employing one-component developers recently, because they are free of deterioration and replacement of carriers and thus permit compactification of a developing device. These developers are made as follows. A resin with a magnetic material dispersed therein is synthesized or crushed in a spherical shape having the weight average diameter of about 3 to 15 .mu.m, or in indefinite shapes to form matrices-called classified particles and, in order to add a further function, powder, called an externally attached agent, of the submicron order is attached to the surface thereof. More specifically, the magnetic material is, for example, magnetite, the resin is, for example, polystyrene, polyester, or polybutadiene, and the externally attached agent is, for example, alumina, silica, strontium titanate, or the like.
Mechanisms at the time of occurrence of fusion of the developer are generally classified under two types; a type of precipitation of the externally attached agent in a film form and a type of adhesion of the classified particles fused.
Since the a-Si light receiving members have high surface hardness, they scarcely suffer degradation of image quality due to the reason of excess shaving of the surface of the light receiving member after repetitive use in ordinary use circumstances. However, the surface of the a-SI light receiving members sometimes has projections due to abnormal growth in the production process thereof. Most of the projections have heights of approximately 2 to 3 .mu.m, but a few projections could have heights over 10 .mu.m. Such projections could damage a cleaning blade. Particularly, a cleaning blade with increased hardness was fragile and was sometimes chipped when damaged at the process speed over 400 mm/sec (which will be called blade chipping hereinafter).
For preventing the blade chipping, a sufficient prevention effect can be achieved, for example, up to about 600 .mu.m/sec by limiting the heights of projections to below 5 to 6 .mu.m. An effective method for implementing it is to process the surface of the light receiving member by polishing means. As for prevention of the fusion of developer, however, it was the status that an improvement in the quality of blade material was expected.
It is also contemplated that the surface of the a-Si light receiving members is scrubbed with the blade itself (5 to 10 .ANG./10,000 copies) and/or with an elastic cleaning roller or the like (about 25 to 50 .ANG./10,000 copies) for removal of transfer or the like of ozone products, thereby removing them. There are, however, desires for efforts toward further stabilization of quality as to the fusion of the developer under the recent circumstances of the decrease in the grain sizes of developers and the increase in the process speed such as the copy speed or the like.
Under such circumstances there are desires for a cleaning system preferably applicable to high-speed electrophotographic apparatus ready for high image quality.
A cleaning method popularly used for cleaning the a-Si base light receiving members is a blade type cleaning method which has high cleaning performance as a cleaning means in general.
This blade type cleaning method, however, could cause uneven shaving of the surface layer of the light receiving member in some cases because of differences in amounts of the developer staying on the blade surface, depending upon differences of character patterns on an original chart. When such uneven shaving occurs, differences are made in incident light amounts because of interference to cause sensitivity unevenness as an electrophotographic characteristic and in turn cause density irregularities of an image in some cases.
Particularly, this phenomenon of the density irregularities becomes more prominent as the grain sizes of the developer become smaller.
There are, however, recent desires for improvement in the image characteristics to higher image quality and the grain sizes of the developer are becoming smaller and smaller under such circumstances. This decrease of the grain sizes of the developer improves the image quality on one hand, but tends to increase the scrubbing power on the other hand. This increase of the scrubbing power could cause passing-through of the residual developer (toner) due to chatter or the like of the cleaning blade and sometimes causes a cleaning failure of a black line pattern.
Further, if frictional resistance is high, frictional heat will rise between the light receiving member and the cleaning blade and there will arise a possibility of the fusion phenomenon that the residual developer used in thermal fixation is firmly attaches to the surface of the light receiving member because of the frictional heat. Particularly, this fusion phenomenon tends to become more prominent in proportion to the decrease in the grain sizes of the developer; it is too trivial to affect the image at the initial stage, but repetitive use could result in gradual growth of fusion around nuclei of small fused developer and forming an image defect of a black line pattern in the image in certain cases.
In addition, as digitization is advanced with development of computers, the percentage of laser printers is also Increasing in the field of electrophotography. A significant feature of such digital copiers is the so-called reverse development in which the developer is placed on only print areas with a laser or an LED array. Since in this development the developer is laid on low-potential portions of the light receiving member, application amounts of the developer in the cleaner part are larger than in the case of analog machines employing the normal development, and it could be a significant cause of promoting the abrasion and the fusion of developer.
It is not easy for users themselves of the electrophotographic apparatus to recover such uneven shaving or fusion. Therefore, a work of serviceman or the like is necessitated, which posed challenges of expense including the cost for replaced parts, the labor cost, etc. and time loss due to stop of the electrophotographic apparatus during the work. They are typical challenges in the electrophotographic apparatus and are significant challenges, which could cause increase of running cost, particularly, in high-speed machines.
Examples of conceivable solutions to such challenges under such circumstances are measures including a method of increasing the urging pressure of the cleaning blade, a method of increasing the hardness of the elastic rubber blade in order to increase the force for scraping off the developer attached to the surface of the light receiving member, and so on. Increasing the hardness of the blade changes the property of the blade from a rubber-like state to a glass state and thus makes the material fragile, so as to shorten the lifetime of the blade. Further, the above methods tend to Increase the frictional force against the surface of the light receiving members so that there are some cases in which the uneven shaving of the surface layer is rather degraded.